Motors are devices that convert electric energy into mechanical energy according to the law of electromagnetic induction, and can be divided into direct current motors and alternating current motors.
A permanent magnet direct current (PMDC) motor is a direct current motor that uses a permanent magnet to create magnetic field. The PMDC motor is widely used in various portable electronic devices or appliances, such as a recorder, a VCD player, an electric gramophone, an electric massager and various toys, and also widely used in automobiles, motorcycles, electric bicycles, battery cars, ships, aviation, machinery and other industries.
With the development of the motor technology, the PMDC motors have been more widely used. The permanent magnet direct current motors will replace the alternating current motors in many applications.
However, different application fields have different requirements for performance of the permanent magnet direct current motors. For example, in a heating, ventilation and air conditioning (HVAC) system, the PMDC motor is used to inject fresh air into a compartment, and is required to have a low noise. FIG. 8 shows an existing PMDC motor used in the HVAC system for automobiles, which includes a housing 100, a stator magnet 200 fixed to an inner surface of the housing 100, and a rotor core 300 disposed in the stator magnet 200. The rotor core 300 includes teeth 301. Windings 302 are wound around the teeth 301. In this permanent magnet direct current motor, a thickness of the stator magnet 200 is relatively small, an outer diameter of the rotor core 300 is relatively large, which is 17.9 mm, and a tooth width of the teeth 301 of the rotor core 300 is also as wide as 4.2 mm. Therefore, the rotor core 300 has a large moment of inertia of the rotor core 300 and can easily produce noise, which cannot satisfy customers' demand for low noise of the automobile HVAC systems.
Hence, it is necessary to improve the existing PMDC motor, so as to effectively reduce the noise generated by the PMDC motor during operation to improve quality of the motor.